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# Metronidazole (Metrogyl)
## Overview
Metronidazole is an antibiotic and antiprotozoal agent effective against anaerobic bacteria and certain protozoa.
## Primary Indications
* **Bacterial Vaginosis:** Treatment of bacterial vaginosis.
* **Trichomoniasis:** Treatment of trichomoniasis.
* **Amebiasis:** Treatment of intestinal amebiasis (amebic dysentery) and extraintestinal amebiasis (e.g., amebic liver abscess).
* **Giardiasis:** Treatment of giardiasis.
* **Anaerobic Bacterial Infections:** Treatment of serious anaerobic bacterial infections (e.g., intra-abdominal infections, skin and soft tissue infections, gynecologic infections, bone and joint infections, CNS infections, lower respiratory tract infections, endocarditis).
* **Pseudomembranous Colitis:** Treatment of Clostridium difficile-associated diarrhea (CDAD).
* **Surgical Prophylaxis:** Preoperative prophylaxis, particularly in colorectal surgery.
* **Helicobacter pylori Eradication:** Part of combination therapy for H. pylori.
## Adult Dosing
* **Bacterial Vaginosis:** 500 mg orally twice daily for 7 days, or a single 2-gram dose orally.
* **Trichomoniasis:** 2 grams orally as a single dose, or 250 mg orally three times daily for 7 days, or 375 mg orally twice daily for 7 days.
* **Amebiasis:**
* Intestinal: 500-650 mg orally three times daily for 5-10 days.
* Extra-intestinal: 500-650 mg orally three times daily for 5-10 days, or 50-100 mg/kg/day (maximum 4 g/day) divided into 3 doses.
* **Giardiasis:** 250 mg orally three times daily for 5-7 days, or 500 mg orally twice daily for 5 days, or 2 grams orally once daily for 3 days.
* **Anaerobic Bacterial Infections:** 500 mg IV or orally every 8 hours. Duration varies by infection, typically 7-14 days. Higher doses (e.g., 750 mg every 8 hours) may be used for severe infections. Maximum dose generally 4 g/day.
* **Pseudomembranous Colitis:** 500 mg orally three times daily.
* **Surgical Prophylaxis:** 1 g IV or 500 mg orally 1-2 hours before surgery, followed by 500 mg orally or IV every 8 hours for up to 24 hours post-operatively.
* **H. pylori Eradication:** Typically 500 mg orally twice daily in combination with other agents for 10-14 days.
## Pediatric Dosing
Dosing in children is often weight-based and depends on the specific indication. Consult pediatric infectious disease guidelines.
* **Giardiasis:** 15 mg/kg/day orally divided into 3 doses (maximum 250 mg/dose), not to exceed 40 mg/kg/day (maximum 2 g/day), for 5-7 days.
* **Amebiasis:** 35-50 mg/kg/day orally divided into 3 doses (maximum 750 mg/dose) for 5-10 days.
* **Anaerobic Bacterial Infections:** 7.5 mg/kg/dose IV or orally every 8 hours. Maximum dose generally 4 g/day.
## Dose Adjustments
* **Hepatic Impairment:** Use with caution. Some sources recommend reducing the dose by 30-50% in severe hepatic impairment. Limited data for IV administration.
* **Renal Impairment:** No dose adjustment is typically necessary for hemodialysis patients. For peritoneal dialysis, no specific recommendations are established, but dose reduction may be considered.
## Contraindications
* Hypersensitivity to metronidazole or other nitroimidazole derivatives.
* Use with disulfiram (within 2 weeks).
* Use during the first trimester of pregnancy, especially for trichomoniasis, unless other options are not feasible.
## Adverse Effects
* **Common:** Nausea, vomiting, diarrhea, abdominal discomfort, metallic taste, headache, dizziness.
* **Serious:** Peripheral neuropathy (especially with prolonged use), seizures, encephalopathy, aseptic meningitis, Stevens-Johnson syndrome, toxic epidermal necrolysis, leukopenia, thrombophlebitis (IV), pancreatitis, superinfection.
* **Disulfiram-like reaction:** Avoid alcohol during treatment and for at least 72 hours after discontinuation due to potential for severe nausea, vomiting, flushing, and tachycardia.
## Key Drug Interactions
* **Warfarin:** Metronidazole can potentiate the anticoagulant effect of warfarin. Monitor INR closely and adjust warfarin dose as needed.
* **Lithium:** Metronidazole can increase lithium levels, potentially leading to toxicity. Monitor lithium levels.
* **Phenytoin/Phenobarbital:** May decrease metronidazole levels.
* **Cyclosporine:** Metronidazole may increase cyclosporine levels.
* **Disulfiram:** Concurrent use can lead to a disulfiram-like reaction.
## Monitoring
* **Clinical response:** Assess for improvement of signs and symptoms of infection.
* **Neurological status:** Monitor for signs of peripheral neuropathy or central nervous system effects, especially with prolonged therapy.
* **Complete blood count (CBC):** May be monitored with prolonged therapy or in patients with compromised bone marrow function.
* **Liver function tests:** Monitor in patients with hepatic impairment.
* **Renal function tests:** Monitor in patients with renal impairment.
## Clinical Pearls
* The metallic taste is a common and often bothersome side effect.
* Alcohol should be strictly avoided during therapy and for at least 72 hours after the last dose due to the disulfiram-like reaction.
* For vaginal use, oral metronidazole is generally preferred over topical formulations for bacterial vaginosis and trichomoniasis for efficacy.
* IV metronidazole can cause thrombophlebitis; slow infusion and dilute solutions are recommended.
* When used for H. pylori, ensure adherence to the full combination therapy regimen.
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*This information is intended for healthcare professionals. Always consult the most current prescribing information and relevant clinical guidelines for complete details.*
